Re-dyeing Hair?

So I dyed my hair 4 weeks ago a dark chocolate brown, color level 3. After shampooing it this long, it has faded to way too reddish of a shade for me. I want to dye it "darkest brown" level 2 tonight. But do I leave it on the whole 30 mins or less cuz it's a darker shade, but only 4 weeks have passed. It's a permanent dye.